Submersible pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Typically, a submersible pumping system includes a number of components, including an electric motor coupled to one or more high performance pump assemblies. Production tubing is connected to the pump assemblies to deliver the petroleum fluids from the subterranean reservoir to a storage facility on the surface. The pump assemblies often employ axially and centrifugally oriented multi-stage turbomachines.
Although widely used, conventional downhole turbomachinery is vulnerable to “gas locking,” which occurs in locations where petroleum fluids include a significant gas to liquid ratio. Gas locking often causes the inefficient operation or complete failure of downhole turbomachinery. The gas-locking phenomenon can be explained by the dynamics of fluid flow through the impeller and diffuser. The streamwise and transverse pressure gradients, streamline curvature and slip between different phases contribute to the segregation of the phases. Upon separation, the gas phase tends to accumulate in certain regions of the flow passage, causing head degradation and gas locking.
Numerous attempts have been made to lessen the adverse effects of gas locking. Gas separator units have been frequently used in conjunction with submersible pump assemblies to reduce the volume of gas in the petroleum fluids being pumped to the surface. In other cases, separate helical “compressor” pumps have been used to reduce the volume of the gas before introducing the petroleum fluid to the primary pumping assembly. Although functional, these prior art solutions require the fabrication and assembly of additional components, decreases the overall efficiency of the submersible pumping system and elevate the risk of mechanical failure.
There is therefore a continued need for an improved pump assembly that effectively and efficiently produces two-phase fluids from subterranean reservoirs. It is to these and other deficiencies in the prior art that the present invention is directed.